Arizona Bureau of Geology and Mineral Technology

Summer 1986

Volcanic

by Stephen J. Reynolds, John W. Welty, andJon E. Spencer Arizona Bureau of Geology and Mineral Technology

Although Arizona lacks active volcanoes, it was the site of massive outpourings of lava and volcanic ash during the recent and more distant geologic past. Volcanism not only formed the oldest rocks in Arizona 1.8 bi11ion years (b.y.) ago, but also constructed the State's highest mountains, the San Francisco Peaks, within the last 3 million years (m.y.). Volcanic rocks are widespread throughout the State and dominate much of its scenery (Figure 1). This article summarizes the Figure 1. Aerialphotograph ofS P Craterandbasaltflow In Ihe San Francisco volcanic volcanic history of Arizona and briefly describes the importance of field, north of Flagstaff The eruption that formed Ihis cinder cone and lava flow volcanic rocks in the State. occurred relatively recently, about 70,000 years ago. Photo by David D. Nations.

A second episode of Precambrian volcanism occurred about 1.1 Volcanic Episodes to 1.2 b,y. ago, but was moreareally restricted and less voluminous than the previous episode. This volcanism is evident in basalt flows and Six major episodes of volcanism are represented within the rhyolite tuffs (compacted volcanic ash) interbedded with sedimentary geologic record of Arizona. These episodes 10cal1y, but unequal1y, rocks ofthe late Precambrian Apache Group nearGlobe and the Unkar affected al1 three of Arizona's geologic-physiographic provinces: Colo­ Group of the Grand Canyon (Figure 2). These rocks accumulated in rado Plateau, Transition Zone, and Basin and Range Province (Peirce, basins within the stable continental interior and were later injected with 1984). Volcanic activity within the last 10 m.y., for example, was intense horizontal sheetlike intrusions, or si11s, of diabase, a dark·colored along the boundarybetween the Colorado Plateau andTransition Zone, igneous rock that forms by crystallization of basaltic magma at depth. butwas less common in other parts ofthe State. Because each volcanic These diabase sills are well displayed in the walls of the Salt River episode was localized, mineral and energy resources related to Canyon northeast of Globe. The presence of basalt flows, tuff, and volcanism are also unequal1y distributed. This unequal distribution has, diabase sills within a continental basin suggests that volcanism and in turn, dramaticallyaffected the settlementofArizona and continues to sedimentation accompanied a period of minor continental rifting. exert some influence on the population distribution. After this second episode, volcanism was evidently absent in The earliest volcanic episode in Arizona occurred during the Arizona for almost 1 by, or more than half of the State's entire geologic Precambrian Era between 1.8 and 1.6 b.y. ago and formed much ofthe history. During this prolonged volcanic quiescence, which includes all continental crustthat underlies the region today. Volcanic rocks formed of the Paleozoic Era (570 to 245 m.y. ago), Arizona was a relatively during this time are most widely exposed in the Transition Zone and stable, topographically subdued region that was intermittently flooded parts of the Basin and Range Province (Figure 2). Volcanism probably by shallow seas. This interval of relative stability was interrupted in the began when the oceanic crustwas pulled apart, creating a rift in the sea early Mesozoic, when volcanic ash and detritus were blown by winds floor from which basalt was erupted. This process of sea-floor and washed by streams into northern Arizona from distant volcanoes to spreading is occurring today along the mid-oceanic ridges circling the the south and west, probably in northern Mexico or southern California Earth. Large volcanic islands, some similarto Hawaii and others similar (Peirce, 1986). The volcanic ash and debris were deposited in the to the Aleutian Islands in Alaska, were built upon the basaltic sea floor. Upper Triassic Chinle Formation and became altered to impart the The central volcanoes erupted basalt and more silica-rich lavas and variegated colors of the Painted Desert and Petrified Forest. ByJurassic were surrounded by aprons of sedimentary debris derived from time (190 m.y. ago), volcanism became widespread in a northwest­ explosive eruptions of volcanic ash and from erosion of the volcanoes. trending volcanic belt that crossed southern Arizona from Douglas to Heatfrom the central volcanic conduits caused water to circulate within Parker (Figure 3). Volcanoes within this belt erupted regionally and around the volcanoes, which led to deposition of mineral deposits extensive rhyolitic tuffs and more localized rhyolitic lavas. The volcanic such as the famous copper-silver-gold ores of Jerome. Col1isions landscape was locally overrun by sand dunes, believed to have between converging volcanic arcs deformed and metamorphosed the migrated southward from the great deserts that existed during volcanic and associated sedimentary rocks, locally converting them deposition of the Lower Jurassic Navajo Sandstone of the Colorado into schist (Anderson, 1986). During and after these collisions, large Plateau. The resulting interbedded Jurassic volcanic rocks and sand­ masses of granitic magma intruded into and helped stabilize the stones are present in the Santa Rita and Baboquivari Mountains of continental crust of the region. southern Arizona and in several mountain ranges near Parker. ---'l'~7-_l_-7::~~j'. --f---r o

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DISTRIBUTION OF PRECAMBRIAN VOLCANIC AND METAVOLCANIC ROCKS IN ARIZONA DISTRIBUTION OF JURASSIC (200-150 m.y.) VOLCANIC ROCKS

Figure 2. Outcrops ofPrecambrian and metamorphosed uolcanic rocks formed during Figure 3. Outcrops ofJurassic uolcanic rocks occurin a northwest-trending belt across the first uolcanic episode (1.6-1.8 b.y. ago) are shown in black. Deformation and southern Arizona. metamorphism underhigh temperatures andpressures hauegenerally conuened these uolcanic rocks into schist or gneiss. Outcrops of rocks formed during the second episode (1.1-1.2 b.y. ago) are too small to show indiuidually. but occur in the Unkar granitic masses in the Santa Catalina Mountains, Baboquivari Moun­ Group in the Grand Canyon area (GC) and in the Apache Group near Globe (AG). tains, and southwestern Arizona. There was a pronounced lull in volcanic activity during the early In Late Jurassic time (145 m.y. ago), volcanism moved westward Tertiary from 50 to 35 m.y. ago (Shafiqullah and others, 1980). This out of Arizona and into coastal California and Baja California, where a interval was followed by a middle Tertiary episode of intense volcanism volcanic arc formed along the continental margin, much like the that covered much of the Basin and Range Province with regional present-day Andes of South America. This volcanism occurred above ash-flow tuffs and more areally restricted rhyolite, andesite, and basalt an east-dipping subduction zone, where a plate of oceanic crust in the flows. During this episode, a single catastrophic eruption west of Pacific Ocean descended into the mantle beneath coastal California Kingman deposited a layer of ash-flow tuff over an area of 35,000 km2 and Mexico. Volcanism continued along the coast during most of the between Peach Springs, Arizona and Barstow, California (Glazner and Cretaceous, whereas southern Arizona was largely free of volcanoes others, 1986). Volcanism swept westward across Arizona between 35 and was locally inundated by shallow seas from the east. and 15 m.y. ago, as the dip of the subducted oceanic plate decreased Arizona's fourth volcanic episode occurred during Late Cretaceous beneath Arizona (Coney and Reynolds, 1977). As a result, middle to early Tertiary time (85 to 45 m.y. ago), when volcanism and Tertiary volcanic rocks are mostly 25 to 35 m.y. old in southeastern associated igneous activity migrated eastward back into Arizona and Arizona, but 15 to 25 m.y. old in western Arizona. These middle Tertiary adjacent New Mexico. This eastward sweep of magmatism was due to a volcanic rocks are widespread throughout the Basin and Range decrease in the dip orangle ofthe subducted oceanic plate beneath the Province (Figure 5) and provide the backdrop for some of the region's region (Coney and Reynolds, 1977). Volcanic rocks ofthis age are most most scenic areas, including the Chiricahua, Galiuro, Superstition, and widely preserved in southeastern Arizona (Figure 4), but originally Hieroglyphic Mountains, Picacho Peak, the Kofa National Wildlife covered parts of western Arizona, where they have been removed by Refuge, Organ Pipe National Monument, and Apache Leap near erosion. This volcanic episode included construction of andesitic Superior. Middle Tertiary volcanic rocks are present, but much less stratovolcanoes, as well as catastrophic caldera collapse that accom­ common, in the Transition Zone and Colorado Plateau. Middle Tertiary panied eruption of large volumes of volcanic ash. Caldera collapse volcanism was locally accompanied by deposition of precious- and locally resulted in the deposition of breccias that contain house-sized base-metal veins from hot fluids that circulated near the volcanic blocks of limestone, granite, and other rocks derived from the walls or centers and along major fault zones. deeper levels of the caldera. Remnants of such calderas are probably The sixth and last major episode ofvolcanism in Arizona occurred present in the Silver Bell, Tucson, and Santa Rita Mountains near during the late Cenozoic since 15 m.y. ago. It coincided with faulting Tucson (Lipman and Sawyer, 1985). During this episode ofvolcanism, that formed many of the deep basins in the Basin and Range Province large porphyry copperdeposits formed in the cooling magma chambers and Transition Zone. In contrast to the previous episode, volcanism underneath the volcanoes. These copper deposits, like the associated largely consisted of basalt flows that are most widely exposed in the volcanic rocks, are most cornman in southeasternArizona, where they Transition Zone and along the southwestern edge of the Colorado escaped complete removal by erosion. Volcanism was followed by Plateau (Figure 6). The basaltic volcanism on the Colorado Plateau was widespread melting of the lower continental crust, which formed large locally accompanied by more silica-rich flows that built the extinct and

2 FIELDNOTES, Summer 1986 MI 0 50 I KM 0 50

DISTRIBUTION OF DISTRIBUTION OF MID-TERTIARY (40-15m.y.) VOLCANIC ROCKS LARAMIDE (80-50 m.y.) VOLCANIC ROCKS

eroded volcanoes of the San Francisco Peaks and Mount Baldy in the White Mountains. The most recent basaltic volcanism, as indicated by the presence of preserved cinder cones, has been largely restricted to the San Francisco, Springerville, and Uinkaret volcanic fields of the Colorado Plateau and the Sentinel, San Bernardino, San Carlos, and Pinacate volcanic fields of the Basin and Range Province. The most recent volcanic eruption in Arizona occurred at Sunset Crater near Flagstaff between the growing seasons of 1064 and 1065A.D. (Smiley, 1958). During each volcanic episode described above, volcanism prob­ ably migrated in a complex manner between different parts ofthe State. The migration of volcanism during the two most recent volcanic episodes is illustrated in Figure 7, which shows the distribution of isotopic age determinations on volcanic and related granitic rocks for different time periods during the last 40 m.y. These maps demonstrate that volcanism resumed in southeastern Arizona approximately 30 to 40 m.y. ago and shifted westward across the State between 30 and 15 m.y. ago. At the start of the late Cenozoic volcanic episode 15 m.y. ago, volcanism progressively migrated to the northeast across theTransition Zone and into the Colorado Plateau (Figure 8). The maps also identify where the most recent volcanism has occurred and, therefore, where there may be a slight potential for future eruptions.

Figure 4. Late Cretaceous to early Tertiary (Laramide) volcanic rocks are common in southeastern Arizona (as are the associated porphyry copperdeposits). but havelargely been eroded from western Arizona.

Figure 5. Middle Tertiary volcanic rocks are most Widespread in the Basin and Range Province.

Figure 6. Late Cenozoic volcanics are abundant in the Transition Zone and south­ DISTRIBUTION OF UPPER CENOZOIC (0-15 m.y.) western edge ofthe Colorado Plateau. but are relatively sparse in the Basin and Range VOLCANIC ROCKS AND VOLCANIC FIELDS Province near Phoenix and Tucson.

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Figure 7. Distribution ofisotopic age determinations on volcanic and related granitic rocks for different time periods during the last 40 m.y_ These maps illustrate how volcanism migrated westward across Arizona between 40 and 15 Ma (million years ago) and then migrated northeastward toward the Colorado Plateau_

Industrial Uses of Volcanic Rocks hydrothermal alteration and structural deformation. Because of this, they have not been quarried for industrial use. A variety of middle Tertiaryvolcanic rocks are used commercially, The six episodes of volcanism have produced a diversity of with those of silicic composition (at least 65 percent SiO by weight) metallic mineral deposits and unusual volcanic rock types that are used z being the most important. Perlite, a rhyolitic glass that contains a as industrial products. Most precious- and base-metal ore deposits in concentric "onion-skin" structure caused by cooling and hydration, Arizona were produced during the early Precambrian, Late Cretaceous­ occurs in many parts of the Basin and Range Province. The term early Tertiary, and middle Tertiary episodes of volcanism and related "perlite" has been traditionally used to describe any naturally occurring emplacement of granitic magmas. In contrast, intrusion of the late volcanic glass that expands when heated to yield a frothy, lightweight Precambrian diabase magmas into the Apache Group near the Salt cellular substance similar in some aspects to popcorn. Perlite with River Canyon and the Unkar Group in the Grand Canyon helped to form excellent expansion (popping) capabilities commonly has thefollowing significant deposits of chrysotile asbestos, magnetite-rich iron ore, and properties: (1) shiny luster; (2) onion-skin texture; (3) few visible uranium (Wrucke and others, 1986). crystals; (4) presence of marekanites; (5) specific gravity (density) of Of the six volcanic episodes, only the mid-Tertiary and late approximately 2.4 gjcc; and (6) 3 to 4 percent water by weight (Wilson Cenozoic events produced rocks that are substantially exploited today. and Roseveare, 1945). Marekanites, obsidian nodules known as Volcanic rocks of Precambrian and Jurassic age have been so variably "Apache tears," are small areas of the rhyolitic glass that lack the metamorphosed and structurally disrupted that their physical and onion-skin texture (Figure 9). The perlites of Arizona have been chemical properties make them unsuitable for most commercial uses. historically or are currently used for lightweight and high-strength The sole exception occurs near Mayer, where schist derived from aggregate, fire-retardant insulation, perlite-gypsum plaster, beverage metamorphosed rhyolite is mined for dimension stone and used in the filtrate, soil conditioner, molding for foundry sands, and filler for paints construction industry as building facade. The qualities that made this and plastics. Perlite occurrences near Picketpost Mountain southwest material attractive to architects are the result of subsequent meta­ of Superior are of primary importance because of large potential morphism rather than the original volcanic processes. Late Cretaceous­ reserves and commercial development (Peirce, 1969). early Tertiary (Laramide) volcanic rocks are confined mostly to Other uses of middle Tertiary volcanic rocks include the following: southeastern Arizona and have commonly undergone considerable (1) pumice mined by the Gila Valley Block Company northeast of

4 FIELDNOTES, Summer 1986 sw PRESCOTT JEROME SEDONA FLAGSTAFF O-,-----l------L------.L------l---=",...----ih=...... -r

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15-L-.L....------..:!:L------'-----==::..J-15 lila Figure 8. Diagram shows the ages ofvolcanic rocks versus their geographic positions along a northeast·southwest Figure 9. View ofmarekanites (blackspoLs), or ''Apache line through Prescott and Flagstaff Volcanism migrated northeastward during the last 15 my. The most recent tears," in a gray matrix ofperlite from the Sil-Flo perlite volcanism occurred slightly northeast of Flagstaff pit west ofSuperior. Photo by John W Welty.

Safford for the fabrication of lightweight concrete block; (2) similar the mineral wealth of Arizona. The large copper deposits and many deposits near Kirkland in central Arizona that were crushed and sized gold-silver veins formed as heated fluids circulated near volcanic for the production of cat litter; (3) an opaque opal known as fire agate in conduits. In addition, a variety of other commercial products such as rhyolitic tuff near Klondyke, Graham County; and (4) basalt southwest perlite, cinders, and lightweight aggregate are currently produced from of Casa Grande that is used in the manufacture of rock-wool insulation volcanic rocks. Because of the diverse ages and types of volcanism in products. Arizona, the potential for future production of volcanic-related com­ Upper Cenozoic volcanism resulted in the development of numer­ modities is great. ous cinder cones, particularly in the San Francisco and White References Mountains volcanic fields, In both of these areas, the cinders display a Anderson, Phillip, 1986, Summary of the Proterozoic plate tectonic evolution of Arizona wide variety of colors from black to magenta. The distribution of and from 1900 to 1600 Ma, in Beatty, Barbara, and Wilkinson, P. A K., eds., Frontiers in differences among the color types are not well understood, although geology and ore deposits of Arizona and the Southwest: Arizona Geological Society the red cinders are thought to be the result of oxidation of black cinders. Digest, v. 16, p. 5·11. Coney, P. J., and Reynolds, S. J., 1977, Cordilleran Benioffzones: Nature, v. 270, p. 403·406. Cinders are mined for use as rip-rap, cinder block, aggregate for road Damon, P. E., Shafiqullah, M., and Leventhal. J. S., 1974, K·Ar chronology for the San base and asphaltic concretes, drilling-mud conditioners, drainage fields Francisco volcanic field and rate oferosion ofthe Little Colorado River, in Karlstrom, T. for septic systems, winter traction on icy roads, and landscaping N. V, and others, eds., Geology of northern Arizona, with notes on archaeology and paleoclimate; pt. 1, regional studies: Geological Society of America, Rocky Mountain (Figure 10). Because the Phoenix area is devoid of cinder deposits, it Section Meeting, Flagstaff. Ariz., 1974, p. 221·235. must import this useful material from the Colorado Plateau region. Glazner, A. F., Nielson, J. E., Howard, K. A, and Miller, D. M., 1986, Correlation ofthe Peach Basalt on Peridot Mesa in the San Carlos volcanic field also contains Springs Tuff, a large-volume Miocene ignimbrite sheet in California and Arizona, in peridot, or gem-quality olivine, which is intermittently sold to rock Cenozoic stratigraphy, structure, and mineralization in the Mohave Desert: Geological Society of Arnerica, Cordilleran Section Annual Meeting, 82nd, Los Angeles, Calif., collectors and stone cutters for jewelry or mineral specimens. 1986, Guidebook and Volume, Trips 5 and 6, p. 65·68. In the San Francisco volcanic field, the Sugarloaf Mountain Lipman, P. W., and Sawyer, D. A, 1985, Mesozoic ash·flow caldera fragments in rhyolite dome erupted 212,000 years ago (Damon and others, 1974). southeastern Arizona and their relationship to porphyry copper deposits: Geology, v. This eruption produced a layer of rhyolitic tuff, which yielded over 13, no. 9, p. 652·656. Peirce, H. W., 1969, Perlite, in Mineral and water resources of Arizona: Arizona Bureau of 200,000 tons of lightweight, high-strength aggregate (pumice) used in Mines Bulletin 180, p. 403-407. the construction of Glen Canyon Dam. Currently the material is sold as ___ 1984, The Mogollon escarpment: Arizona Bureau of Geology and Mineral lightweight aggregate and for landscaping, and Arizona Tufflite, Inc. is Technology Fieldnotes, v. 14, no. 2, p. 8·11. ___ 1986, Paleogeographic linkage between Arizona's physiographic provinces, in planning to market this material as a pozzolan. Pozzolans are siliceous Beatty, Barbara, and Wilkinson, P. A K., eds., Frontiers in geology and ore deposits of materials that, when finely ground (to -325 mesh), will form a "natural" Arizona and the Southwest: Arizona Geological Society Digest, v. 16, p. 74·82. cement in the presence of water and lime. Other pozzolans are found Shafiqullah, M., Damon, P. E., Lynch, D. J., Reynolds, S. J., Rehrig, W. A, and Raymond, R. near Williams in upper Cenozoic rocks and near Bouse and Safford in H., 1980, K·Ar geochronology and geologic history of southwestern Arizona and adjacent areas, in Jenney, J. P., and Stone, Claudia, eds., Studies in western Arizona: mid-Tertiary rocks. Arizona Geological Society Digest, v. 12, p. 201·260. Many volcanic eruptions are accompanied by explosive outpour­ Smiley, T. L., 1958, The geologyand dating ofSunset Crater, Flagstaff, Arizona: NewMexico ings of volcanic ash, such as that erupted from Mount St. Helens in Geological Society Guidebook, 9th Field Conference, p. 186·190. Wilson, E. D., and Roseveare, G. H., 1945, Arizona perlite: Arizona Bureau ofMines Circular 1980. When this ash, which is composed of minute particles ofvolcanic 12,10 p. glass, is deposited in a lake or other bodyofwater, it is locally altered to Wrucke, C. T., Otton,J. K., and Desborough, G. A, 1986, Summaryand origin ofthe mineral useful products. Two of these products, bentonite clay and the zeolite commodities in the middle Proterozoic Apache Group in central Arizona, in Beatty, mineral chabazite, are mined in Arizona and exported for use elsewhere_ Barbara, and Wilkinson, P. A K., eds., Frontiers in geology and ore deposits ofArizona Bentonite mining in east-central Arizona began in 1924 and presently and the Southwest: Arizona Geological Society Digest, v. 16, p. 12-17. produces about 40,000 tons peryear from beds of altered volcanic ash of late Cenozoic age. The bentonite is processed into desiccants, thickeners, and acid-activated clay products. The Bowie chabazite deposit of southeasternArizona, also of late Cenozoic age, is mined for use as an activated molecular-sieve material. This deposit has yielded the largest mined tonnage of any natural zeolite in the United States, with a total product value of about $30 million since 1962.

Conclusion Arizona has experienced a complex volcanic history that has spanned 1.8 b.y. of geologic time. In addition to helping shape the Figure 10. Layerofred cinders at the Us. Forest Service Porter Mountain pit northeast diverse and beautiful scenery of the State, volcanism and related ofLakeside, Navajo County. The grate in the lowerright is used to size the cindersbefore processes are responsible for many useful products as well as much of shipping. Photo by John W Welty.

FIELDNOTES, Summer 1986 5